DEPARTMENT OF MUNICIPAL ARBORICULTURE 251 



The spacing of the trees and the numbers given them are 

 also indicated. 



Value of Tree Census. The maps are found to be ex- 

 tremely valuable office records in a great many ways. When 

 a request is made for attention to a certain tree on a street, 

 the tree warden can immediately find out the species and 

 condition of the tree by referring to his field book and maps. 

 When it is proposed to plant certain streets which have 

 some existing trees, the records can be used to determine the 

 trees that are to be removed, and adequate provision made 

 for the planting of new ones. 



Records of street-trees are invaluable in organizing a 

 campaign against an insect pest attacking a certain species. 

 By knowing the number and distribution of affected trees 

 coming under his jurisdiction, the tree warden can make 

 ample provision for their treatment and direct the work 

 intelligently. In most cases the period of time is limited 

 during which the extermination of insect pests may be done 

 most effectively. The treatment of elm-trees for the elm- 

 leaf beetle is a case in point. The insect can be controlled 

 only by spraying, and the time when that may be done most 

 effectively is limited to two or three weeks. When the tree 

 warden knows the total number of elm-trees in his city and 

 the number on each street he can accomplish the most work 

 within the limited time. 



The field books and the maps can be used to compute the 

 number of the trees necessary to plant on a street. From the 

 records of the conditions of the trees it will usually be possi- 

 ble to determine what trees are to be cut down. Thus from 

 the descriptions of the trees numbered 10, 19, and 20 on 

 "Shepard Street," it is seen that they are not fit to retain, 

 and they are checked off as trees to be removed. 



